Selected Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Total Revenues	$ 75.6	$ 67.9	$ 71.1	$ 76.7	$ 84.6	$ 96.2	$ 79.8	$ 65.9	$ 291.3	$ 326.5	$ 250.3
Income Before Income Taxes	72.3	58.8	66.3	68.0	72.4	90.3	60.8	49.3	265.4	272.8	149.1
Net income	72.3	58.8	66.3	68.0	72.5	90.6	60.7	49.1	265.4	272.9	148.9
Net Income Attributable to the Partnership	69.5	56.3	63.8	55.3	57.0	54.3	32.2	23.6	244.9	167.1	13.4
Limited Partners' Interest in Net Income Attributable to the Partnership	$ 59.8	$ 49.1	$ 58.8	$ 52.2	$ 54.7	$ 52.8	$ 31.5	$ 23.1	$ 219.9	$ 162.1	$ 13.1
Net income per Limited Partner Unit - Basic and Diluted (in dollars per share)	$ 0.34	$ 0.28	$ 0.35	$ 0.36	$ 0.38	$ 0.37	$ 0.23	$ 0.17